Field of the Invention
The present invention relates to a developing device, a process cartridge, and an image forming apparatus that employ an electrophotographic method.
Description of the Related Art
In electrophotographic image forming apparatuses such as a laser beam printer, a copying machine, first, a photosensitive drum is uniformly electrically charged by a charge unit. Then, the electrically-charged photosensitive drum is irradiated with light (e.g. laser light) corresponding to image information, thereby forming an electrostatic latent image on the photosensitive drum. Thereafter, a developer bearing member of a developing device supplies developer to the electrostatic latent image to visualize the electrostatic latent image as a developed image. Further, the developed image on the photosensitive drum is transferred onto a recording material such as a sheet to form an image on the recording material.
Conventionally, a corona charging method has popularly been used as a means for electrically charging a photosensitive drum. In recent years, a contact charging method, as typified by a charging roller capable of reducing the voltage of a power source and also reducing generation of ozone, is increasingly used.
Further, as to cleaning techniques, it is common to employ a configuration in which toner (or developer) that is not transferred and remains on a photosensitive drum is removed from a surface of the photosensitive drum by a cleaning device and then stored as waste toner in the apparatus. However, from the points of view of environmental protection, efficient use of resources, and apparatus size reduction, it is desirable not to produce waste toner. In view of the foregoing, U.S. Patent Publication Application No. 2005/0214031 discusses a method whereby residual untransferred toner that is not transferred onto a recording material and remains on a photosensitive drum is cleaned by a developing device simultaneously with development. In this method, the residual untransferred toner on the photosensitive drum can be collected by the developing device and reused. This method is known as a cleanerless method.
However, in a case where a contact charging member is used in a cleanerless image forming apparatus, toner remaining on a photosensitive drum after passing through a transfer position sometimes adheres to the contact charging member. A contaminated contact charging member may adversely affect image formation.